| Precision agriculture aviation technology is one of the core technologies of modern agriculture in China.This technology is based on the different sites with different operating conditions,According to the change of coordinate and time,the operating parameters of aeronautical vehicle are adjusted to obtain the optimal green plant protection effect,in which variable spray is the most effective implementation link.With the rapid development of UAV technology,The variable-spraying technology of UAV has been developed gradually,but the key technology is still immature.In this paper,the research status of variable spray technology at home and abroad is reviewed.By means of flight acceleration information and spray pressure,the precision of spray is calibrated,the working efficiency is improved,and the best effect of pesticide application reduction is obtained by adopting flow control method.The key technology is to collect flight acceleration,spray flow rate and PID control algorithm to control flight speed..At the same time,the PWM control method is used to control the working time of the liquid pump to achieve real-time control of the spray flow rate.The variable spray system of multi-rotor UAV is designed and verified by variable spray test.Firstly,on the basis of analyzing the research status of variable spray technology at home and abroad,this paper summarizes the surface variable spray technology and UAV variable spray technology,and studies the control scheme of adopting PWM pulse width regulation mode.The effect of velocity on droplet distribution of special aviation nozzle is verified by experiments.According to the structure of UAV and the result of indoor test,the frame of variable system is determined.The singlechip and sensor are selected,the optimal selection is obtained,and the control system is built.PID is used to adjust the parameters and modify the algorithm to improve the function of the system.Finally,through the system debugging and performance test,the rationality and feasibility of the system research and development are verified preliminarily,and the flow variable control test is carried out after the research and improvement.The relationship model of the relationshipmodel of the flight speed and the spray flow rate and the relationship model of the PWM duty ratio and the flow rate are determined by the experimental research.(1)The type 22.1184 MHz crystal oscillator is used to select the crystal oscillator of the main control system.(2)The expression of the relationship between the velocity and the flow rate is established through the test experiment of the flight speed and spray flow of the UAV,the experimental results show that the error between the actual flow data and the theoretical data at different flight speeds is 0.833%,which can realize variable spray according to the requirements.(3)Based on the analysis of duty cycle and flow rate,the relevant model of adjustable PWM duty cycle is built,andthe pesticide spray test was carried out in different stages.The variable spraying system was tested and the actual spraying results were obtained under the conditions of 0.3L/min?0.4L/min?0.5L/min and 0.6L/min.The error was 8.73%? 4.74%and 0.83%,respectively,which achieved the purpose of variable spray control. |
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